Welded stainless steel tubes are produced by various kinds of welding methods such as high frequency resistance welding, laser welding, TIG welding, and plasma welding. Among those, the TIG welding is a welding method which is most widely used because a cost of equipment is inexpensive and excellent welding quality can be achieved.
In a case where a welded tube is produced by TIG welding, arc discharge is generated between an end of a tungsten electrode and a welding target material, and the welding target material is welded by heat of the arc discharge. Here, stability of the arc discharge is one of factors that influence the welding quality. The arc discharge is an electromagnetic phenomenon, and therefore the welding target material is demanded to be physically stable in order to maintain stable arc discharge that is emitted from the end of the tungsten electrode toward the welding target material which is an electric conductor.